unfoldIndex.cpp

inline size_t unfoldIndex(const std::vector<size_t>& index, const std::vector<size_t>& shape) noexcept
{
	size_t s = 0;
	size_t v = 1;
	assert(index.size() == shape.size());
	for(int i=(int)index.size()-1;i>=0;i--) {
		v *= (i==(int)index.size()-1?1:shape[i+1]);
		s += index[i] * v;
	}

	return s;
}

//Example:
//a[16*321*321]
//a[unfoldIndex({1,1,1}, {16,321,321})]